How is Johnny Manziel a RS freshman if he's a junior in school?

He is a junior by classification only. Took summer school and enrolled early and also redshirted. Maybe even came to college with college credit hours. Don't know. Point it, it doesn't matter. He has 3 years to play if he wants.

Summer School. Most athletes take 12 hours over the summer.

AP classes/summer classes.

My daughter was a junior when she started her third semester of school. Pretty common, I'd think.

He also enrolled early. He finished HS in three and a half years and enrolled at A&M in January of his senior year in high school, to get spring ball in. So, while he is only a freshmen in terms of eligibility, he has been on the A&M campus for 4 semesters now. Add in summer school, and he is a Junior academically.

He was an early enrollee who redshirted... if he took classes in the summer, that's two semesters under his belt before most entering freshman have taken a class...

this isn't that difficult to understand.

Same reason Aaron Murray has already graduated and is half way through a phd program, and still has another year of eligibility.

It's Magic.